X-ray monochromator of linear type



y T969 TERUICHI TOM'URA 3,445,653

X-RAY MONOCHROMATOR OF LINEAR TYPE Filed Oct. 4, 1965 Sheet I of s L= 2RSine M zdsme=rfl 3 I Lg"? INVENTOR. TERUICHI Tom uRn BY J! ZLIWJ mum 0,1969 TERUICHI TOMURA 3,445,653

XRAY MONOCHROMATOR OF LINEAR TYPE Sheet 2 01'3 Filed on. 4, 1965 FIG.3

INVENTOR. TERomHl ToMuRA BY -A alum I'll mailer May 20, 1969 TERUICHITQMURA 5 X-RAY MONOCkROMATOR OF LINEAR TYPE Filed Oct. 4. 1965 sum 3 ora INVENTOR. HER we H 1 76M 0 R H I BY (Slu -J mas/em United StatesPatent Office 3,445,653 Patented May 28, 1969 3,445,653 X-RAYMONOCI-HIOMATOR F LINEAR TYPE Teruichi Tomura, Kodaira-shi, Tokyo-to,Japan, assignor to Kabushiki Kaisha Hitachi Seisakusho, Tokyo-to, Japan,a joint-stock company Filed Oct. 4, 1965, Ser. No. 492,616 Claimspriority, application Japan, Oct. 10, 1964, 39/ 57,528 Int. Cl. G01n23/20 US. Cl. 25051.5 4 Claims ABSTRACT OF THE DISCLOSURE A linear typeX-ray monochromator constructed by a first link connecting four pointsconsisting of a first pivot disposed at one point spaced apart by" aspecific distance from the center of a Rowland circle, a first terminalpoint, on which an analyzing crystal is mounted, a second terminalpoint, and a second pivot disposed at the intersection point of theRowland circle and an auxiliary circle having the same radius as that ofthe Rowland circle and a center thereof at the point spaced apart fromthe center point by a specific distance, both points being fittedmovably along two straight lines intersecting at an X-ray source to forma certain angle and always to exist on the circumference of the Rowlandcircle; and a second link connecting three points consisting of a thirdpivot disposed at a point on a straightway guide movably fitted on thesecond pivot so as to be spaced apart from the point by a distance equalto the distance between the X-ray source and the first terminal point,and a third terminal point from the point on the straightway guide by adistance equal to the above specific distance; and one end of a leverhaving a length equal to the above specific distance is secured to thepoint, and the other end is movably fitted on the straightway guide,whereby a focusing point of the diffracted X-ray can be obtained on thecircumference of the Rowland circle.

This invention relates to an X-ray monochromator, and more particularlyto a new X-ray monochromator, in which an analyzing crystal and an X-raydetector are respectively constructed to move along straight lines witha constant mutual distance therebetween, the straight lines intersectingwith each other in an X-ray source at a certain constant angletherebetween, so that the crystal, the X-ray source and the X-raydetector may be always maintained on a Rowland circle.

It is a general object of the present invention to overcome certaindifficulties which accompany conventional X-ray monochromators.

More specifically, an object of the invention is to provide an X-raymonochromator of linear type which facilitates shifting of the Rowlandcircle to a suitable position along a circular locus.

Another object of the invention is to provide an X-ray monochromatorwherein various parts such as the crystal, links, and pulleys can beassembled with separated pivots, whereby the thickness of the entireapparatus can be substantially reduced.

A further object of the invention is to provide an X-ray monochromatorof a construction and arrangement, wherein no part exists in front ofthe bent crystal in case an asymmetrically cut crystal is used, wherebyanalysis of shorter wavelengths becomes possible'and the range of usecan be expanded.

The nature, principle, and details of the persent invention will be moreclearly apparent from the following detailed description when it is readin conjunction with the accompanying drawings, in which like parts aredesignated by like reference numerals and characters, and in which:

FIGS. 1 and 2 are schematic geometric views for description respectivelyof focusing and linear type X-ray spectroscopic methods;

FIG. 3 is a schematic geometric view for description of the principle ofthe present invention; and FIGS. 4, 5, and 6 are schematic geometricviews show- 1ng preferred embodiments of the X-ray monochromatoraccording to the invention.

As conducive to a full understanding and appreciation of the nature andutility of the present invention, the following brief consideration ofthe principles of the focusing and linear type X-ray spectroscopicmethods is presented.

Referring to FIG. 1 indicating the principle of a focusing type X-raymonochromator, if a crystal having curved net planes as designated byreference numeral 4 (arcs of concentric circles with their centers atpoint 3) is used, X-ray beams passing through a point 1 will bediffracted and will always pass through a point 2. That is, divergentX-rays passing through the point 1 (or X-rays emitted from point 1 as anX-ray source) are assumed to be diffracted over the entire span of thecurved net planes of. the crystal, whereby sensitivity of the X-ray monochromator would theoretically be increased. However, since it isdifiicult to produce such a crystal with net planes so curved, and thearrangement or construction of the X-ray detector becomes verycomplicated when using this crystal, such crystal cannot be used inpractice for X-ray analysing purposes. Accordingly, bent or curvedcrystals of either a symmetrical type having the part 5 of theabove-mentioned curved net planes, or a symmetrical type having the part6 are generally used.

In this case, the position 1 of the X-ray emission point, the bentcrystal 5 (or 6), and the focusing point 2 are always on the same circle8, which is generally called the Rowland circle. The angles a and 13 atthe circumference both of which are subtended by the are 1-3 are equalto each other, and their complementary angles are also equal. Therefore,the angle subtended by the are 1-7 becomes 20, which is equal to thatsubtended by the are 2-7.

That is, both central angles are equal, and each is equal to two timesthe X-ray grazing angle 0 (the angle of intersection between theaforementioned net plane which participates in the diffraction and theincident X-ray) as indicated in FIG. 1, therefore, the chord L (lengthof the segment 10) and the chord La (length of the segment 11) areequal, and, moreover, this chord L is proportional to the wavelength ofthe diffracted X-rays.

FIG. 2 indicates the principle of linear type X-ray spectroscopy whichwill now be considered. If a bent crystal 5 is shifted as indicated bydesignations 5a and 5b along a straight line 10, and its Rowland circle8 is revolved so as to pass always through the X-ray emission point '1as indicated by designations 8a and 8b, the focusing conditions will beconstantly satisfied. In this case, the focusing point 2 in movingthrough corresponding positions 2a and 2b describes a complicated pathresembling a part of a lernniscate as indicated by doted line 12.

Since the direction of the analyzed X-ray beam from source 1 is constantin this system, this system is suitable for use in electron probemicroanalyzers and fluorescent X-ray analyzers, in which constancy ofX-ray take-off angle is important, and, furthermore, has the advantageof afford-ing direct reading of the X-ray wavelength by the displacementdistance.

In FIG. 1, as the Rowland circle 8 is shifted through positions 8a and8b, the corresponding positions of its 3 center 9 are 9a and 9b, andthose of a slit 13- and detector 14 are 13a, and 14a, 14b, respectively.

The conventional X-ray monochromator of linear type as above describedis so constructed that the center 9 of the Rowland circle undergoes acircular motion around the X-ray emission source 1. However, theabove-mentioned direct control of the circular movement of the Rowlandcircile center is very diflicult to be attained because of restrictionsimposed by actual construction of the X-ray source. For example, inorder to obtain such circular locus 9, 9a, 9b of the Rowland circlecenter as shown in FIG. 2 it is necessary to take the point 1 as thecenter of the circular locus, though the specimen to be analyzed must beplaced at this point 1. Therefore, a pivot shaft or other elements forallowing the direct circular movement of the Rowland circle center mustbe disposed at this point 1, so as not to interfere with the positioningof the specimen at the point 1 as well as projeotion of the incidentelectron beam 15 with respect to the specimen therefor. But it is verydifficult in practice to realize such mechanism. As alternativemeasures, an arcuate guide, etc., have been used so as to establish thecircular locus of the Rowland circle center. However, such alternativemechanism is obstructive to the positioning of other elements, forexample, employment of specimen fine moving mechanisms is restricted bythe establishment of the arcuate guide, whereby the range of the X-raywavelength to be analyzed is greatly restricted. The above-mentionedarcuate guide is obstructed by mechanisms such as that for causing finemovements of the specimen, and in many such cases, restriction of thewavelength range of X-rays which can be analyzed is imposed.

The present invention contemplates the elimination of the abovedescribed difficulties by providing an X-ray monochromator of lineartype wherein the principal operation of the linear type X-raymonochromator as shown in FIG. 2 can be obtained by using more usefulmeans than the conventional device, so that great many numbers ofmechanical elements concentrated at the point 1 of the X-ray source maybe reduced.

The principle of the present invention will first be described inconjunction with FIG. 3. In this FIG. 3, a Rowland circle 8 is shown tohave a center 9 and a given radius. According to the present invention,an auxiliary circle 21 is employed in partially overlapping relationwith the Rowland circle 8. This auxiliary circle 21 has a center 17 andthe same radius as that of the Rowland circle and also producesintersecting points, one of which is designated by the numeral 19.

Now assume that the angles 7-9-19 and 9-1917 are designated as g and .5respectively, a point such as point 22 that produces an angle 7-9-22 tobe equal to 2 may be obtained on the Rowland circle 8. Once the point 22has been obtained, a point is obtained by eX- tending a straight line 40having a length as long as the distance between the point 1 and 22 fromthe point 19 to allow intersection of the straight line 40 with theauxiliary circle 21. From point 20, a point 18 is then obtained toproduce a triangle A20-17-18 which is congruent with a triangleA19-9-17. Finally, the intersection of a straight line having a lengthas long as the distance between the points 18 and 20 with the line 40having produced the required point 2. This relation will be explained asfollows.

The Rowland circle center 9 is assumed to have been shifted to the point17, the focusing point 2 is also assumed to have been shifted to a point18 on the auxiliary circle 21 since the distance between the focusingpoint 2 and the point 8 is equal to the distance between the Rowlandcircle 9 and the auxiliary circle center 17. Therefore, the intersectionbetween the points 19 and 17, and 9 and 2 respectively, is designated bynumeral 48. The angles 19-48-2 and 19-17-18 are equal to each other. The

4 angle 7-9-2 is, therefore, shown in the following equation.

On the other hand, the angle 1-9-7 is represented by the followingequation.

Since the triangles A1-9-22 and A19-17-20 are congruent, the angle1-9-22 is equal to the angle 19-'17-20, so that This signifies that thepoint 2 is positioned symmetrically with the point 1 with respect to thepoint 7.

Now, the operability of the present invention is described when theinventive principle is in moving condition. First, an auxiliary circle21 is to be determined to partially overlap with the Rowland circle 8.The center 17 thereof and the mutually intersecting point 19 areobtained. A first link is provided to connect the abovementioned points17, 19, and 7 and a discretionary point 35 to each other with a mutuallyfixed relationship therebetween. This link is so facilitated that thepoints 7 and 35 are constrained to move along straight lines 38 and 49.It is a well established geometrical theorem that these points 7 and 35always position themselves on the Rowland circle in a shifted statewhich is shifted around the point 1. Accordingly, once the point 7 isfixed at a certain position on the straight line 38, a point 22 will beobtained to satisfy the angular requirement as mentioned above, i.e.,r2, and the distance between the points 1 and 22 is taken on astraightway guide 40 to fix the distance of a movable point 20 which isreciprocally movable along the guide from the point 19. This guide 40 isrotatably mounted around the point 19. A second link connecting betweenthe point 17 and 20 with the same distance as the radius of the Rowlandcircle 8 and the auxiliary circle 21 is provided and the point 18 isassociated therewith to form an isoceles triangle which is congruentwith the triangle A9-19-1'7. Finaly, point 2 is movably mounted to theguide 40 which is constrained to move along the guide with a link 39 offixed length, the length of which is the same as that of the base linkof the isosceles triangle. According to the present invention, the point22 may be in accord with either the point 7 or the point 19.

The required components of the X-ray monchrornator according to thepresent invention are as follows:

(a) A first link for connecting four points consisting of a first pivotdisposed at a given point 17 spaced apart by a specific distance fromthe center 9 of a Rowland circle 8, a first terminal point 7 at which ananalyzing crystal is mounted, a second terminal point 35, points 7 and35 being on the circumference of the Rowland circle 8, and a secondpivot disposed at the intersection point 14 of the Rowland circle andthe auxiliary circle 21 having the same radius as the Rowland circle anda center at the point 17;

(b) Means for securing the point 7 and the point 35 to be respectivelymovable along two straight lines intersecting at an X-ray source to forma given angle on the circumference of the Rowland circle 8;

-(c) A straightway guide secured to the second pivot;

(d) A second link for connecting the three points consisting of a thirdpivot movably disposed at a point 20 on the straightway guide spacedapart from the point 19 by the distance equal to that between the X-raysource and the point 7, or the point 19, or a point 22 at the other endof the base triangle A7-9-22 having a vertex angle o'(o'=2) 9-1917)-(7-9-19) and a third terminal 'and the other is movably disposed on thestraightway guide;

(f) Means for maintaining an X-ray detector disposed outside of theRowland circle and on the extension of a straight line connectingbetween the point 7 and the intersection point 2 (focusing point) of thestraightway guide and the other end of the lever; and

(g) Means for linearly moving the third pivot and the other end of leverin cooperation with the first link.

One embodiment of the invention as applied to an X-ray microanalyzer isshown in FIG. 4 (where 5:25), in which the same reference numerals andcharacters as those of FIG. 3 are used. In addition, an electron beam15, an electron lens 33, and a specimen 16 are shown.

In FIG. 4, analyzing crystal 5 is provided at the terminal point 7 of afirst link 31 for connecting points 717-359 with each other, where therespective points 7 and 35 are movably disposed along two straight linesand 23 which intersect with each other at an X-ray source 1 to form acertain angle 5 therebetween. It is apparent from the above descriptionthat the distance between the points 7 and 35 is kept constant.Accordingly, it is possible to cause the points 7, 1 and 35 to exist onthe Rowland circle 8 whose center is always on a circumference of acircular locus around the X-ray source 1 having the same radius as thatof the Rowland circle. The second link 32 for connecting points 17-20-18is rotatable around the point 17, and the point 20 of the link 32 issecured movably on a straightway guide 24 whose one end is rotatablysecured to the point 19. Also, pulleys 26 and 27 are respectivelydisposed on the points 7 and 19 and lever 39 is secured between thepoint 18 and the movable point 2 (focusing point) on the straightwayguide 24. Moreover, a tension member is provided to pass around pulleys26, 27 and 28 as shown in FIG. 4 and is secured to the point 20 at oneend thereof. An X-ray detector 30 is disposed outside of the Rowlandcircle 8 on the extension of a straight line connecting both points 2and 7. In such construction, the end point 2 of the lever 39 will alwayscoincide with the X-ray focusing point, whereby X-rays diffracted by thecrystal 5 can be properly focused at the focusing point. Therefore, thediffracted X-rays pass through a slit 29 mounted at the point 2 and aredetected by the detector 30.

In this case, since the rotational angle of the link 31 is set to beequal to that of the quide 2, by using the pulleys 26 and 27 having thesame diameter, the lengths of the tension member 25 wrapped respectivelyabout the pulleys are equal to each other and the respective wrappeddirections are opposite. Therefore, regardless of the position of theRowland circle 8, the distance between the point '19 and 20 ismaintained by the tension member 25 so as to be equal to that betweenthe points 1 and 7. Here, since the angle .5 shown in FIG. 3 is selectedto be equal to 2g in the example shown in FIG. 4, the point 22 of FIG. 3will coincide with the point 7.

Then, if a third link 32 connecting points 17-20-18 and a straightwayguide 24 are engaged respectively with pivots provided at fixed points17 and 27 fixed to the second link 31, and the distance between points19 and 20 is maintained equal to the distance between points 1 and 5 bymeans of a tension member 25, the extremity point 2 of a link 39 mountedon the pivot 18 will always coincide with the X-ray focusing point as isapparent from the foregoing consideration.

Then, since the angular relationships are so selected that (angle7-219)= /2 (angle 7-919)= /2 and that =2, X-rays can be focused at adetector 30, irrespective of the movement of the Rowland circle, bymounting a slit 29 at the point 2 and the detector 30 on a lineangularly displaced by the fixed angle 5; from the axis of thestraightway guide 24. Since the angle 5; shown in FIG. 3

is selected to equal 2g in the instant example shown in FIG. 4, thepoint 22 of FIG. 3 coincides with the point 7.

The above mentioned tension member 25 is passed as shown in FIG. 4around pulleys 26 and 27, the diameters of which are so selected thatthe lengths of the tension member 25 wrapped respectively about thepulleys are equal and, being of opposite direction, are mutuallycancelled since the rotational velocity of the link 31 around the pivot17 is equal to the rotational velocity of the guide 24 around the pivot19 relative to the link 31.

In order to prevent this tension from slackening, it is necessary toimpart tension thereto by means such as a spring (not shown) at point20. It is not necessary, of course, to construct the links 31 and 32with only straight lines, other configurations being suitable for theselinks provided that they establish the correct positions of the pivots.

Another embodiment of the invention as shown in FIG. 5 illustrates thecase wherein the angular relationship in FIG. 3 is expressable by =2,that is, and point 22 is caused to coincide with point 19. Morespecifically, in place of the tension member 25 of the example shown inFIG. 4, there is provided a tension member 25a such as to establish adistance between said center of the bent crystal and the focusing pointwhich distance is equal to the distance between the X-ray point sourceand said intersection of said two circles. The construction of the otherparts are the same as those shown in FIG. 4.

In this case, however, in order to provide compensation for the numberof windings of the tension member around the pulleys, a pulley 27a and apulley 41 of a diameter twice that of the pulley 27a are used as shownsince, with a rotational ratio of the link 31, guide 24, and link 32 of1:2:3, the rotational difierence between the guide 24 and the link 32 is321=1, and the extreme end of the tension members 25a is fixed to thelink 32. Furthermore, by using pulleys of the same diameter as 27a atpoints 20, 18, and 2, any difference in the lengths of the tensionmember can be cancelled out.

A further embodiment of the invention as shown in FIG. 6 is suitable forthe case wherein an asymmetrically cut crystal is used which is placedat the point of intersection of said two circles and wherein a link fordriving this crystal is provided. In this case, since there is nospecial mechanical part in front of the bent crystal 6, and the segment10 is proportional to the Wavelength of the X-rays to be diffracted,direct reading of the X-ray wavelength is possible at point 47 to whichpoint 7 has been parallelly moved. For this reason, the bent crystal 6is indirectly driven by means of links 44 and 45. The fact that at thistime the movement of the pivot 47 is proportional to the wavelength willbe quite apparent from the fact that the imaginary point 7 is beingparallelly moved. That is, except for the mechanism for moving the bentcrystal 6, the construction of the instant example is the same as thatshown in FIG. 5.

According to the present invention as described above, it is possible toavoid obstruction by parts such as an electron lens by causing thecentre of the Rowland circle to shift to a suitable position, wherebythe distance between the specimen to be measured and the analyzingcrystal, that is, the range of usable X-ray wavelengths, is widened.Furthermore, since the various parts such as the crystal, links, andpulleys can be assembled in dispersed state, the thickness of the entireapparatus can be reduced relative to that of a conventional apparatuswherein these parts are concentrated at one point, whereby the presentinvention is highly suitable for cases where a large number ofspectroscopes are used in combination.

The present invention afiords further advantages such as the possibilityof construction wherein no parts exist in front of the bent crystal inthe case where an asymmetrically cut crystal is used, whereby dispersionof short wavelengths becomes possible, and the range of use is expanded.Accordingly, the present invention is highly effective in applicationsto instruments such as X-ray probe microanalyzers and fluorescent X-rayanalyzers.

It should be understood, of course, that the foregoing disclosurerelates to only preferred embodiments of the invention and that it isintended to cover all changes and modifications of the examples of theinvention herein chosen for the purposes of the disclosure, which do notconstitute departures from the spirit and scope of the invention as setforth in the appended claims.

What I claim is:

1. A linear type X-ray monochromator comprising: an X-ray source; ananalyzing crystal; an X-ray detector; a first link for connecting fourpoints consisting of a first pivot disposed at a certain point (17)spaced apart by a distance smaller than the diameter of the Rowlandcircle from the center (9) of a Rowland circle (8); a first terminalpoint (7 on which the crystal is mounted; a second terminal point (35),said first and second terminal points (7 and 35) and the X-ray sourcebeing positioned on the circumference of the Rowland circle, and asecond pivot disposed at an intersection point (19) of the Rowlandcircle and an auxiliary circle (21) having the same radius as that ofthe Rowland circle and a center thereof at the certain point (17); meansfor reciprocably constraining the first and second terminal point (7 and35) to move along two straight lines, respectively, which intersect eachother at an angle smaller than 180 at the X-ray source; a straightwayguide pivotally secured at one end thereof to the second pivot; a secondlink pivotally mounted to the first link at the first pivot forconnecting the three points consisting of the first pivot, a thirdmovable pivot disposed at a second point (20) which is constrained tomove on the straightway guide so as to be spaced apart from theintersection point (19) by a distance equal to the distance from theX-ray source to such a third point (22) which provides an isoscelestriangle A7-9-22 having a vertex angle 0', where 0' is designated bya=2( 91917)( 7919), and a third terminal point (18) so that an isoscelestriangle AIS-1740 congruent to the triangle A7-9-22 may be obtained; alever (39) having a length equal to the distance between the center andsaid certain point (9 and 17), one of its ends being pivotally fitted tothe third terminal point (18) and the other constrained to move alongthe straightway guide; means for maintaining the X-ray detector outsideof the Rowland circle in a straight line connecting the first terminalpoint (7) and the intersection point positioned at the intersection ofthe straightway guide and the other end of the lever, the X-ray focusingslit being disposed at a focusing point (2); and means for linearlymoving the third pivot and the other end of the lever in cooperationwith the first link.

2. The X-ray monochromator according to claim 1, wherein the thirdmovable pivot is spaced apart from the intersection point (19) by adistance equal to the distance from the X-ray source to the firstterminal point (7 3. The X-ray monochromator according to claim 1,wherein the third movable pivot is spaced apart from the intersectionpoint (19) by a distance equal to the distance from the X-ray source tothe intersection point (19).

4. The X-ray monochromator according to claim 1, which further comprisesa tension member, one end of which is fixed and the other secured to thesecond point (20), and at least two pulleys about which the tensionmember is wrapped in opposite directions.

References Cited UNITED STATES PATENTS 2,898,469 8/1959 Rose 250-5l.53,073,952 1/1963 Rose 25051.5 3,123,710 3/1964 Neuhaus 250--51.5

RALPH G. NILSON, Primary Examiner.

S. C. SHEAR, Assistant Examiner.

US. Cl. X.R.

